This invention relates to planarizing pads in mechanical and/or chemical-mechanical planarization of microelectronic substrates.
Mechanical and chemical-mechanical planarization processes (collectively xe2x80x9cCMPxe2x80x9d) are used in the manufacturing of electronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic device substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly. FIG. 1 schematically illustrates an existing web-format planarizing machine 10 for planarizing a substrate 12. The planarizing machine 10 has a support table 14 with a top-panel 16 at a workstation where an operative portion (A) of a planarizing pad 40 is positioned. The top-panel 16 is generally a rigid plate to provide a flat, solid surface to which a particular section of the planarizing pad 40 may be secured during planarization.
The planarizing machine 10 also has a plurality of rollers to guide, position and hold the planarizing pad 40 over the top-panel 16. The rollers include a supply roller 20, idler rollers 21, guide rollers 22, and a take-up roller 23. The supply roller 20 carries an unused or pre-operative portion of the planarizing pad 40, and the take-up roller 23 carries a used or post-operative portion of the planarizing pad 40. Additionally, the left idler roller 21 and the upper guide roller 22 stretch the planarizing pad 40 over the top-panel 16 to hold the planarizing pad 40 stationary during operation. A motor (not shown) generally drives the take-up roller 23 to sequentially advance the planarizing pad 40 across the top-panel 16, and the motor can also drive the supply roller 20. Accordingly, clean pre-operative sections of the planarizing pad 40 may be quickly substituted for used sections to provide a consistent surface for planarizing and/or cleaning the substrate 12.
The web-format planarizing machine 10 also has a carrier assembly 30 that controls and protects the substrate 12 during planarization. The carrier assembly 30 generally has a substrate holder 32 to pick up, hold and release the substrate 12 at appropriate stages of the planarizing process. Several nozzles 33 attached to the substrate holder 32 dispense a planarizing solution 44 onto a planarizing surface 42 of the planarizing pad 40. The carrier assembly 30 also generally has a support gantry 34 carrying a drive assembly 35 that can translate along the gantry 34. The drive assembly 35 generally has an actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The aim 38 carries the substrate holder 32 via a terminal shaft 39 such that the drive assembly 35 orbits the substrate holder 32 about an axis Bxe2x80x94B (as indicated by arrow R1). The terminal shaft 39 may also rotate the substrate holder 32 about its central axis Cxe2x80x94C (as indicated by arrow R2).
The planarizing pad 40 and the planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The planarizing pad 40 used in the web-format planarizing machine 10 is typically a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution is a xe2x80x9cclean solutionxe2x80x9d without abrasive particles because the abrasive particles are fixedly distributed across the planarizing surface 42 of the planarizing pad 40. In other applications, the planarizing pad 40 may be a non-abrasive pad without abrasive particles that is composed of a polymeric material (e.g., polyurethane) or other suitable materials. The planarizing solutions 44 used with the non-abrasive planarizing pads are typically CMP slurries with abrasive particles and chemicals to remove material from a substrate.
To planarize the substrate 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate 12 against the planarizing surface 42 of the planarizing pad 40 in the presence of the planarizing solution 44. The drive assembly 35 then orbits the substrate holder 32 about the axis Bxe2x80x94B, and optionally rotates the substrate holder 32 about the axis Cxe2x80x94C, to translate the substrate 12 across the planarizing surface 42. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate 12.
The CMP processes should consistently and accurately produce a uniformly planar surface on the substrate assembly to enable precise fabrication of circuits and photo-patterns. During the fabrication of transistors, contacts, interconnects and other features, many substrate assemblies develop large xe2x80x9cstep heightsxe2x80x9d that create a highly topographic surface across the substrate assembly. Such highly topographical surfaces can impair the accuracy of subsequent photolithographic procedures and other processes that are necessary for forming sub-micron features. For example, it is difficult to accurately focus photo patterns to within tolerances approaching 0.1 micron on topographic substrate surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical substrate surface into a highly uniform, planar substrate surface at various stages of manufacturing the microelectronic devices.
One problem with conventional CMP methods is that the planarizing surface 42 of the planarizing pad 40 can wear unevenly or become glazed with accumulations of slurry and/or material removed from the substrate 12 or the planarizing pad 40. One conventional approach to address this problem is to condition the planarizing pad 40 by abrading the planarizing surface 42 with an abrasive disk (not shown). In a typical conditioning cycle, the abrasive disk removes accumulations of waste matter and also removes a layer of material from the pad 40. A drawback with this approach is that the equipment required for conditioning the planarizing pad 40 adds complexity to the planarizing machine 10. Moreover, if the conditioning operation is performed separately from the planarizing operation, it reduces the time that the planarizing pad 40 is available for planarizing substrates. Conventional conditioning processes can thus limit the overall efficiency and throughput of the apparatus.
An additional drawback of methods that condition pads with a conditioning stone is that it is difficult to condition pads with grooves or small voids without destroying the grooves. Conditioning stones, for example, may produce inconsistent distributions of grooves on the planarizing surface of a planarizing pad from one planarizing cycle to another. Conditioning stones may also change the depth or the width of existing grooves over the life of a planarizing pad. Conditioning planarizing pads with conditioning stones may thus produce a non-uniform or inconsistent distribution of slurry under a microelectronic device substrate assembly. Therefore, conditioning stones often cause planarizing pads to produce inconsistent polishing rates over the life of the pads.
One approach to address this drawback is to eliminate the need to condition the pad by making the planarizing surface or the entire planarizing pad disposable. For example, U.S. Pat. No. 6,139,402, which is herein incorporated by reference, discloses a disposable planarizing pad film made from materials such as Mylar or polycarbonate. The pads disclosed in U.S. Pat. No. 6,139,402 can have microfeatures of different heights that entrap small volumes of an abrasive slurry and maintain the slurry in contact with the substrate. The microfeatures can be formed using a variety of techniques, such as embossing or photo-patterning. Although disposable pads have many good applications, they do not address the problems of conditioning non-disposable pads with conditioning stones, and the disposable pads may not be suitable for all CMP applications. Therefore, there is still a need for developing planarizing pads and conditioning processes that provide consistent results over the life of non-disposable planarizing pads.
The present invention is directed toward planarizing pads for planarizing microelectronic substrates, planarizing machines with planarizing pads, methods for making planarizing pads, and methods for planarizing the microelectronic substrates. In one embodiment, a planarizing pad for mechanical or chemical-mechanical planarization includes a base section and a plurality of embedded sections. The base section has a planarizing surface and it is composed of a first material. The embedded sections are arranged in a desired pattern of voids or grooves for holding a desired distribution of planarizing solution under a substrate assembly. Each embedded section has a top surface below the planarizing surface to define a void in the base section. As such, the plurality of embedded sections define a pattern of voids in the base section. The embedded sections are composed of a second material that is selectively removable from the first material.
One process for making a planarizing pad in accordance with an embodiment of the invention includes forming a pad body by constructing the embedded sections in the base section. This embodiment for making a planarizing pad can further include removing an incremental portion of the embedded sections from the base section without removing all of the material of the embedded sections. By removing only an incremental portion of the embedded sections, this procedure creates the plurality of voids in the base section and leaves the remaining portions of the embedded sections in the base section. After the pad is used to planarize one or more substrate assemblies and the voids are filled with waste matter or the planarizing surface wears down, an etchant can be deposited on the pad to subsequently etch another incremental portion of the embedded sections faster than the base section to reform the voids over the embedded sections. The planarizing pad can thus be chemically conditioned in manner that provides a consistent pattern and size of voids over the life of the planarizing pad.
In one particular embodiment for making a planarizing pad, the pad body initially comprises a photo-sensitive material that becomes more soluble in a selected etchant upon exposure to a particular radiation (e.g., light). The procedure for constructing the embedded sections in the base section can comprise irradiating portions of the base section corresponding to the desired pattern of voids with the selected radiation. The unexposed portions of the pad body can define the first material of the base section, and the exposed portions of the pad body can change into the second material to define the embedded sections. The exposure time of the light is set to change the first material into the second material to the selected depth within the base section. The embedded sections generally extend to depth that is greater than the desired depth of the voids to provide enough of the second material for incrementally reforming the voids over several conditioning cycles.